This invention relates to an entirely automatically operating apparatus for the automatic taking and preparation of a liquid sample for the determination of the number of cells or particles in suspension in a liquid medium.
A large number of reactions or processes require continuous monitoring of the number of cells or particles present in the operational liquid medium.
There are concerned, for instance, continuous controls of particle size in the production of a product or of the number of cells in suspension in the preparation of a fermented beverage such as beer in which the development of the fermentation phase plays an important role in the quality of the final product.
As a matter of fact, the seed yeast population and its development during the fermentation are considered essential parameters, the value and variations of which must be known.
Thus, the brewing industry has seen the appearance, based on the application of the principle of counting the number of particles which was discovered by Coulter, of an industrial particle-counter which makes it possible to monitor the population during the course of the different phases of the fermentation.
The sampled suspension of yeast, which has been previously diluted in a special electrolyte, is placed in a cylindrical receptacle. This electrolyte forms an electrical resistance between two electrodes, one of which is within a probe which extends into the receptacle and the other outside the said probe within the receptacle.
The probe is immersed in the solution or suspension to be studied. It has a calibrated opening perpendicular to its wall through which the electrolyte and the yeast cells pass, the yeast cells upon each of their passes modifying the electric resistance between the two electrodes, since the conductivity of the particles is different from that of the electrolyte.
As for the peripheral units, they consist essentially of a tube or column of mercury which assures a sufficient vacuum to aspirate a given constant volume of electrolyte out through the measurement orifice; they also comprise visualization and counting members.
As indicated, each pass causes a variation in resistivity of the electric measurement circuit. Each instantaneous variation provides an electric pulse which is electronically counted, whereupon its size is analyzed.
This equipment does great service in breweries; however, its operation still requires a good deal of human intervention, for instance preparation of the electrolyte by a laboratory assistant, no automatic recording of the measurements, etc., and the performance of this apparatus, in view of the degree if automation of the production lines, is inadequate.